The present invention relates to a preloading bearing unit for use with spindle means or the like, and more particularly to such a preloading bearing unit that can be conveniently controlled to impart one of three different preloading pressures.
In order to eliminate the occurrence of a clearance in between a spindle (revolving shaft) and an antifriction bearing, a preloading means may be installed. However, regular preloading bearing means are not adjustable. Adjustable preloading means are seen in U.S. Pat. Nos. 5,388,917 and 5,803,619. However, these two designs still have drawbacks as follows:
1. The preloading pressure can only be adjusted between two levels, namely, the low preloading pressure level and the high preloading pressure level. PA0 2. The hydraulic fluid pressure has to be controlled when adjusting the preloading pressure. PA0 3. Because these design commonly use a single annular hydraulic cylinder to achieve preloading pressure control, the moving parts of the preloading device tend to be stuck.